A flow switch is a mechanical instrument that is used to control the flow of air, steam or liquid. Flow switches work by sending trip signals to another device (a pump for example) within the system, telling it to shut off or to turn on, which will further protect it from damage and for cooling circuit protection. Flow switches determine if flow is above or below a certain rate, known as a set point. The set point can either be adjustable or fixed, depending on the specification of the individual instrument. When the set point is reached, the response is often the actuation of an electric circuit. Once tripped, the flow switch stays in its new state until the fall falls below the set point.